Embodiments of the present invention generally relate to methods and systems for providing alarm systems. Typical building fire alarm systems include a number of fire detectors positioned throughout a building. Signals from those detectors are monitored by a system controller, which, upon sensing an alarm condition, sounds audible alarms throughout the building. Flashing light strobes may also be positioned throughout the building to provide a visual alarm indication. The audible alarms and strobes are typically connected across common power lines on a notification circuit.
In a typical alarm system within a building, such as a fire or burglar alarm system, many types of sensors, detectors, lights, strobes, sounders and other associated devices may be located throughout the building as part of the alarm system. Groups of these devices are often wired together along one or more pairs of electrical lines used to supply power and communications to the devices. A group of such devices wired on a commonly shared pair of lines is often referred to as a line of devices. Many separate lines of devices typically connect back to a control panel that controls the overall operation of the alarm system. A line of devices is usually associated with a certain zone of the building and/or a certain type of device. For example, one floor of a multi-story building may have all of its smoke detectors wired together on a line that connects back to the control panel.
The current practice is to power fire alarm systems from the AC line (primary power) and to have batteries as the secondary power source in the event of AC failure. This method has several disadvantages. First, the standby batteries require periodic testing. The National Fire Protection Association (NFPA), 1 Batterymarch Park, Quincy, Mass. 02169-7471 requires that batteries be tested twice per year. The preferred method is to fully discharge the batteries. This requires that a service technician be on site to conduct the battery test. This is expensive, since it involves labor costs.
Various other methods for testing batteries under load are in common use; however, these methods are deficient in that they do not fully test the battery. These methods do not fully discharge the batteries, but rather discharge the battery slightly. For example, a common method includes switching a load across the batteries. In one example, the load switched is 10 amperes with a 25 Ah battery being used. The test is run periodically—say every 30 minutes—for 10 seconds. This is because more severe discharge rates would jeopardize recharging the battery quickly enough to meet NFPA requirements. A discharge of 10 amperes for 10 seconds represents 0.1522% of the total capacity of a 25 Ah battery. Discharging 0.1522% of battery capacity is not adequate to accurately measure the battery state. Discharging such a small fraction of battery capacity provides little information regarding the condition of a battery. So, this type of battery test is ineffective. Worse, this type of test can build a false sense of security that the alarm system is capable of monitoring battery capacity.
What would therefore be beneficial would be to provide improved power for an alarm system. What would also be beneficial would be to better monitor the capacity of batteries in an alarm system.